Drowning

From the Adult Intensive Care Unit, Hospital Municipal Miguel Couto, and Corpo de Bombeiros Militar — both in Rio de Janeiro (D.S.); the Society to Prevent People from Drowning, Amsterdam (J.J.L.M.B.); the Royal Life Saving Society UK, Broom (A.J.H.); and Florida Hospital and the University of South Florida — both in Tampa (J.P.O.). Address reprint requests to Dr. Szpilman at Av. das Américas 3555, Bloco 2, Sala 302, Barra da Tijuca, Rio de Janeiro, 22631-003 Brazil, or at david@ szpilman.com.


PATHOPH YSIOL O GY OF DROW NING
When a drowning person can no longer keep his or her airway clear, water entering the mouth is voluntarily spat out or swallowed. The next conscious response is to hold one's breath, but this lasts for no more than about a minute. 16 When the inspiratory drive is too high to resist, some amount of water is aspirated into the airways, and coughing occurs as a reflex response. Sometimes laryngospasm occurs, but in such cases, it is rapidly terminated by the onset of brain hypoxia. If the person is not rescued, aspiration of water continues, and hypoxemia quickly leads to loss of consciousness and apnea. The sequence of cardiacrhythm deterioration is usually tachycardia followed by bradycardia, pulseless electrical activity, and, finally, asystole. 17,18 The whole drowning process, from submersion or immersion to cardiac arrest, usually occurs in seconds to a few minutes, but in unusual situations, such as hypothermia or drowning in ice water, this process can last for an hour. 19 If the person is rescued alive, the clinical picture is determined predominantly by the amount of water that has been aspirated and its effects. Water in the alveoli causes surfactant dysfunction and washout. Aspiration of salt water and aspiration of fresh water cause similar degrees of injury, 17 although with differences in osmotic gradients. In either situation, the effect of the osmotic gradient on the very delicate alveolar-capillary membrane disrupts the integrity of the membrane, increases its permeability, and exacerbates fluid, plasma, and electrolyte shifts. 17 The clinical picture of the damage caused to the alveolar-capillary membrane is a massive, often bloodstained, pulmonary edema that decreases the exchange of oxygen and carbon dioxide. 17,20,21 The combined effects of fluids in the lungs, loss of surfactant, and increased permeability of the alveolar-capillary membrane result in decreased lung compliance, increased regions of very low or zero ventilation to perfusion in the lungs, atelectasis, and bronchospasm. 17 If cardiopulmonary resuscitation (CPR) is required, the risk of neurologic damage is similar to that in other instances of cardiac arrest. However, hypothermia associated with drowning can provide a protective mechanism that allows persons to survive prolonged submersion episodes. Hypothermia can reduce the consumption of oxygen in the brain, delaying cellular anoxia and ATP depletion. Hypothermia reduces the electrical and metabolic activity of the brain in a temperaturedependent fashion. The rate of cerebral oxygen consumption is reduced by approximately 5% for each reduction of 1°C in temperature within the range of 37°C to 20°C. 22 Many persons who are drowning are able to help themselves or are rescued in time by bystanders or professional rescuers. In areas where lifeguards operate, less than 6% of all rescued persons need medical attention 4 and just 0.5% need CPR. 21 In one report of rescues by bystanders, almost 30% of persons rescued from drowning required CPR. 23 Untrained rescuers must also avoid drowning 23 and, if at all possible, should provide help from out of the water. Safe rescue techniques include reaching to the drowning person with an object such as a pole, towel, or tree branch or throwing a buoyant object. These quick, safe responses are often neglected and should be taught as part of water safety. It is essential to call for emergency medical services and to undertake rescue and resuscitation immediately. 23 If conscious, the person should be brought to land, and basic life support should be started as soon as possible. 22 For a person who is unconscious, in-water resuscitation may increase the likelihood of a favorable outcome by a factor of more than three, as compared with taking the time to bring the person to land. 24 However, inwater resuscitation is possible only when attempted by a highly trained rescuer, and it consists of ventilation alone. Attempts at chest compression are futile as long as the rescuer and drowning person are in deep water, so assessment for a pulse does not serve any purpose. 24 Drowning persons with only respiratory arrest usually respond after a few rescue breaths. If there is no response, the person should be assumed to be in cardiac arrest and be taken as quickly as possible to dry land, where effective CPR can be initiated. 24 Injuries to the cervical spine occur in less than 0.5% of persons who are drowning, and immobilization of the spine in the water is indicated only in cases in which head or neck injury is strongly suspected (e.g., accidents involving diving, waterskiing, surfing, or watercraft). 25 When rescuing a person from the water, rescuers should try to maintain the person in a vertical position while keeping the airway open, which helps to prevent vomiting and further aspiration of water and stomach contents. 26

INI T I A L R E SUSCI TAT ION ON L A ND
Once on land, the person who has drowned should be placed in a supine position, with the trunk and head at the same level (usually parallel to the shoreline), and the standard checks for responsiveness and breathing should be carried out. 24 If the person is unconscious but breathing, the recovery position (lateral decubitus) should be used. 26 If the person is not breathing, rescue ventilation is essential. Unlike primary cardiac arrest, drowning can produce a gasping pattern or apnea while the heart is still beating, and the person may need only ventilation. 21, [27][28][29] Cardiac arrest from drowning is due primarily to lack of oxygen. [28][29][30] For this reason, it is important that CPR follow the traditional airwaybreathing-circulation (ABC) sequence, rather than the circulation-airway-breathing (CAB) sequence, starting with five initial rescue breaths, followed by 30 chest compressions, and continuing with two rescue breaths and 30 compressions until signs of life reappear, the rescuer becomes exhausted, or advanced life support becomes available. In cases of drowning, the European Resuscitation Council recommends five initial rescue breaths instead of two because the initial ventilations can be more difficult to achieve, since water in the airways can interfere with effective alveolar expansion. 29,31 CPR with chest compression only is not advised in persons who have drowned. [28][29][30] The most frequent complication during a resuscitation attempt is the regurgitation of stomach contents, which occurs in more than 65% of persons who require rescue breathing alone and in 86% of those who require CPR. 32 The presence of vomitus in the airway often results in further aspiration injury and impairment of oxygenation. 24 Active efforts to expel water from the airway (by means of abdominal thrusts or placing the person head down) should be avoided because they delay the initiation of ventilation and greatly increase the risk of vomiting, with a significant increase in mortality. 24,26 The resuscitation of drowning per-sons often takes place under difficult and quite varied circumstances. There may be problems in bringing the person to dry land, and the delay until the arrival of emergency medical services may be considerable. On the other hand, drowning persons are generally young, and the rate of successful resuscitation is higher among young persons than among older persons, often because hypothermia affects young people more quickly than adults, so the chances of successful resuscitation may increase. 18,23,33 A DVA NCED PR EHOSPI TA L C A R E In addition to providing immediate basic life support, it is important to alert advanced-life-support teams as soon as possible. Because of the wide variety of clinical presentations of drowning, a classification system of six grades, with higher numbers indicating more severe impairment, can help to stratify risk and guide interventions (Fig. 1). 21, 34 A person with pulmonary damage may initially be able to maintain adequate oxygenation through an abnormally high respiratory rate and can be treated by the administration of oxygen by face mask at a rate of 15 liters of oxygen per minute. Early intubation and mechanical ventilation are indicated when the person shows signs of deterioration or fatigue (grade 3 or 4). 21 Once intubated, most persons can be oxygenated and ventilated effectively. Although copious pulmonary-edema This classification system can help to stratify risk and guide interventions. The likelihood of survivability was calculated on the basis of time from the site of drowning until hospital discharge. Information is based on a retrospective review of 41,279 rescues recorded by lifeguards, of which 94% (38,975 cases) were just rescues (no water aspiration); less than 6% of these cases (1831) involved the receipt of medical attention, but 1% (473) were not reported with sufficient information to classify the grade of presentation. 21, 34 Of the 1831 cases that received medical attention at the Drowning Resuscitation Center in Rio de Janeiro during the period from 1972 through 1991, 65% were classified as a grade 1 presentation (1189 cases), 18% as grade 2 (338), 3% as grade 3 (58), 2% as grade 4 (36), 1% as grade 5 (25), and 10% as grade 6 (185). 4 ABC denotes airway-breathing-circulation, and CPR cardiopulmonary resuscitation. fluid may appear in the endotracheal tube, suctioning can disturb oxygenation and should be balanced against the need to ventilate and oxygenate. 35,36 Providers of prehospital care should ensure that there is adequate oxygenation to maintain arterial saturation between 92% and 96%, while also ensuring adequate chest rise during ventilation. 37 Ventilation with positive end-expiratory pressure should be initiated as soon as possible to increase oxygenation. 35 Peripheral venous access is the preferred route for drug administration in the prehospital setting. Intraosseous access is an alternative route. Endotracheal administration of drugs is not recommended. 28 If hypotension is not corrected by oxygenation, a rapid crystalloid infusion should be administered, regardless of whether salt water or fresh water has been inhaled. 17 The presenting rhythm in cases of cardiac arrest after drowning (grade 6) is usually asystole or pulseless electrical activity. Ventricular fibrillation is rarely reported but may occur if there is a history of coronary artery disease, if there has been use of norepinephrine or epinephrine (which may increase myocardial irritability), or in the presence of severe hypothermia. 18 During CPR, if ventilation and chest compression do not result in cardiac activity, a series of intravenous doses of norepinephrine or epinephrine, at an individual dose of 1 mg (or 0.01 mg per kilogram of body weight) can be considered. Because of the mechanisms of cardiac arrest due to hypoxia and the effects of hypothermia, a higher subsequent dose, although controversal, 38 may be considered if the initial doses are ineffective.
The cost-effectiveness of providing an automated external defibrillator (AED) at sites of aquatic activity has been debated. The predominant cardiac-arrest rhythm in drowning is asystole. 39 Of course, cardiac arrests at aquatic sites occur from causes other than drowning, and the availability of an AED may be lifesaving. 39 Table 1 summarizes the recommendations on when to begin CPR and how long it should be maintained in cases of drowning.

C A R E IN THE EMERGENC Y DEPA R TMEN T
The majority of drowning persons aspirate only small amounts of water, if any, and will recover spontaneously. Less than 6% of all persons who are rescued by lifeguards need medical attention in a hospital. 21 Once the airway has been secured, oxygenation has been improved, the circulation has been stabilized, and a gastric tube has been inserted, thermal insulation of the patient should be instituted. This is followed by physical examination, chest radiography, and measurement of arterial blood gases. Metabolic acidosis occurs in the majority of patients and is usually corrected by the patient's spontaneous effort to increase minute ventilation or by setting a higher minute ventilation (30 to 35 liters per minute) or a higher peak inspiratory pressure (35 cm of water) on the mechanical ventilator. 20 Routine use of sodium bicarbonate is not recommended. The recorded history of events surrounding the drowning incident should include information on the rescue and resuscitation activities and any current or previous illness. 15 Drowning is sometimes precipitated by an injury or medical condition (e.g., trauma, seizure, or cardiac arrhythmia), and such conditions affect treatment decisions. 21, 40 If the person remains unresponsive without an obvious cause, a toxicologic investigation and computed tomography of the head and neck should be considered. 41 Measurements of electrolytes, blood urea nitrogen, creatinine, and hematocrit are rarely helpful; abnormalities are unusual, 20 and correction of electrolyte imbalance is rarely needed. 42 Persons who have good arterial oxygenation without adjuvant therapy and who have no other associated morbidity can be safely discharged. Hospitalization is recommended for all patients with a presentation of grade 2 to 6. For most pa-

RESPIRATORY SYSTEM
In the ICU, the current treatment of persons who have been rescued from drowning resembles that of patients with the acute respiratory distress syndrome (ARDS). Guidelines for ventilation in ARDS should be followed. However, since the pulmonary lesion is caused by a temporary and local injury, patients with pulmonary distress due to a drowning incident tend to recover much faster than patients with ARDS, and late pulmonary sequelae are uncommon. 35 It is usually best not to initiate weaning from mechanical ventilation for at least 24 hours, even when gas exchange appears to be adequate (ratio of the partial pressure of arterial oxygen to the fraction of inspired oxygen, >250). The local pulmonary injury may not have resolved sufficiently, and pulmonary edema may recur, necessitating reintubation and leading to a prolonged hospital stay and further morbidity. 43 There is very little evidence concerning the value of glucocorticoid therapy for reducing pulmonary injury. It may have a beneficial effect on bronchospasm but should be considered only after a trial of bronchodilators has failed. 44 Pneumonia is often misdiagnosed initially because of the early radiographic appearance of water in the lungs. In a series of hospitalized cases, only 12% of persons rescued from drowning had pneumonia and needed treatment with antibiotic agents. 45 Prophylactically administered antibiotics tend to select more resistant and aggressive organisms. 46 It is best to monitor patients daily for definite fever, sustained leukocytosis, persistent or new pulmonary infiltrates, and leukocyte response in the tracheal aspirate, with culture and sensitivity testing of sputum specimens obtained daily from the aspirate. In addition, bronchoscopy may be performed to monitor selected patients for pulmonary infection and, on rare occasions, is used for therapeutic clearing of mucus plugs or solid material. 47 Early-onset pneumonia can be due to the aspiration of polluted water, endogenous flora, or gastric contents. Aspiration of swimming-pool water rarely results in pneumonia. 45 The risk of pneumonia increases during prolonged mechanical ventilation and can be detected by the third or fourth day of hospitalization, when pulmonary edema has nearly resolved. 45 Pneumonia is often related to nosocomial pathogens. Once a diagnosis is made, empirical therapy with broad-spectrum antibiotics, covering the most predictable gramnegative and gram-positive pathogens, should be started, 45 and definitive therapy should be substituted once the results of culture and sensitivity testing are available. Fungal and anaerobic infections should be considered but can await culture results.
In some patients, pulmonary function deteriorates so dramatically that adequate oxygenation can be maintained only with the use of extracorporeal membrane oxygenation. For these critically ill patients, artificial surfactant, 48 inhaled nitric oxide, 49 and partial liquid ventilation with perfluorocarbons 50 are under investigation; none of these treatments can be recommended now.

CIRCULATORY SYSTEM
In most persons who have been rescued from drowning, the circulation becomes adequate after oxygenation, rapid crystalloid infusion, and restoration of normal body temperature. 17,35 Early cardiac dysfunction can occur in patients with a Early basic life support and advanced life support improve outcome 21, 24,33,54 During drowning, a reduction of brain temperature by 10°C decreases ATP consumption by approximately 50%, doubling the duration of time that the brain can survive 55 Duration of submersion and risk of death or severe neurologic impairment after hospital discharge 19,21,24,32 0-5 min -10% 6-10 min -56% 11-25 min -88% >25 min -nearly 100% Signs of brain-stem injury predict death or severe neurologic sequelae 21, 24,33,41 Prognostic factors are important in the counseling of family members and are crucial in informing decisions regarding more aggressive cerebral resuscitation therapies 51 presentation of grade 4 to 6, 17 which adds a cardiogenic component to the noncardiogenic pulmonary edema. No evidence supports the use of a specific fluid therapy, diuretics, or water restriction 27 in persons who have been rescued from drowning in salt water or fresh water. 17 If volume replacement with a crystalloid infusion fails to restore hemodynamic adequacy, echocardiography can help inform decisions about the use of inotropic agents, vasopressors, or both. 27

NEUROLOGIC SYSTEM
Permanent neurologic damage is the most worrisome outcome in persons who have been resuscitated after a drowning incident. According to the recommendations of a consensus group, 51 persons who are comatose or have neurologic dete-rioration should undergo intensive assessment and care; the goals are to achieve normal values for glucose, partial pressure of arterial oxygen, and partial pressure of carbon dioxide, with avoidance of any situation that increases brain metabolism. Induced hypothermia with the core temperature maintained between 32°C and 34°C for 24 hours may be neuroprotective. 51 In some cases, hypothermia reflects a prolonged submersion time and a poor prognosis. In other cases, early hypothermia is an important reason why survival without neurologic damage is possible. 19,29,49 Recent reports on drowning have documented good outcomes with the use of therapeutic induction of hypothermia after resuscitation, despite a predicted poor outcome. 28,52 The paradox in resuscitation after drowning is that a person with hypothermia needs to be warmed initially in order to be effectively resuscitated but then may benefit from induced therapeutic hypothermia after successful resuscitation.

UNUSUAL COMPLICATIONS
A systemic inflammatory response syndrome after resuscitation has been reported in persons who have been rescued from drowning, but this should not be misinterpreted as infection. Sepsis and disseminated intravascular coagulation are possible complications during the first 72 hours after resuscitation. 27 Renal insufficiency or failure is rare but can occur as a result of anoxia, shock, myoglobinuria, or hemoglobinuria. 53 The most important predictors of the outcome after resuscitation are summarized in Table 2.

PR E V EN T ION
Every drowning signals the failure of the most effective intervention - namely, prevention. 56 Table  3 summarizes recreational safety messages that are based on evidence and expert opinion. 56 It is estimated that more than 85% of cases of drowning can be prevented by supervision, swimming instruction, technology, regulation, and public education. 57 Dr. Bierens reports receiving payment from the Royal Dutch Lifeboat Institute for coordinating a training program; and Dr. Handley, serving as an expert witness in civil litigation cases in the United Kingdom and receiving publishing royalties from the Royal Life Saving Society UK. No other potential conflict of interest relevant to this article was reported.
Disclosure forms provided by the authors are available with the full text of this article at NEJM.org. Know how to stay away from rip currents, which are involved in more than 85% of drowning events at the beach 27

Keep others safe
Help and encourage others, especially children, to learn swimming and watersafety survival skills Fence in a pool on four sides and install a self-closing, self-latching gate, measures that reduce the incidence of drowning by 50 to 70% 27 Provide a warning sign for shallow water in a pool 27